Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $121.73   3.709%   $126.245   $126.25   $126.25   $126.20  
  Purchase #2 $241.94   12.343%   $271.8027   $271.80   $271.80   $271.80  
  Purchase #3 $80.80   8.572%   $87.7262   $87.73   $87.75   $87.70  
  Purchase #4 $211.49   8.667%   $229.8198   $229.82   $229.80   $229.80  
  Purchase #5 $245.60   7.600%   $264.2656   $264.27   $264.25   $264.30  
  Purchase #6 $234.37   9.421%   $256.45   $256.45   $256.45   $256.50  
  Purchase #7 $58.76   10.428%   $64.8875   $64.89   $64.90   $64.90  
  7 purchase totals = $1,194.69       $1,301.1968   $1,301.21   $1,301.20   $1,301.20